1. Field of the Invention
The present invention relates to a multi-stage piston actuator in which a single stem is provided with a plurality of pistons and, in particular, it relates to a separation wall structure within a cylinder thereof.
2. Description of the Related Art
A known multi-stage piston actuator is used as, for example, a multi-stage piston valve in which an increased valve opening or closing force can be obtained from a small valve opening or closing pressure. In such a multi-stage piston valve, a plurality of chambers corresponding to the pistons are formed by a separation wall or walls in a cylinder, so that valve opening or closing pressure is applied to each chamber.
In general, the separation wall within the cylinder of the multi-stage piston valve is in the form of a piston-like separation wall which is fitted in, and secured to, the cylinder, or in the form of an integral separation wall integrally formed with the cylinder which is split into a plurality of cylinder sections by cutting the cylinder sections. However, the manufacturing cost of the piston-like separation wall and the integral separation wall is high, and it is difficult to make the multi-stage piston valve thin or small. Moreover, the piston-like separation wall fitted in the cylinder requires a special seal member, such as an O-ring to establish a fluid-tight connection between the separation wall and the inner wall surface of the cylinder.
It is an object of the present invention to eliminate the above-mentioned drawbacks of the prior art by providing a small, thin and inexpensive multi-stage piston actuator.
To achieve the object mentioned above, according to the present invention, a multi-stage piston actuator is provided, including an operation stem, a plurality of pistons provided on the operation stem at different axial positions, a cylinder in which the pistons are slidably fitted, and a separation wall provided within the cylinder, which defines pressure chambers corresponding to the pistons. The separation wall is made of a cup-shaped member which is provided with a central cylindrical portion in which the operation stem slides, a peripheral cylindrical portion which is fitted in, and secured to, an inner wall surface of the cylinder, and a circular disc portion which connects the central cylindrical portion and the peripheral cylindrical portion.
Preferably, the peripheral cylindrical portion of the cup-shaped separation wall member and the inner wall surface of the cylinder are snugly fitted without a seal member therebetween, so that no air leakage occurs between the peripheral cylindrical portion of the cup-shaped separation wall member and the inner wall surface of the cylinder.
According to another aspect of the present invention, a double-piston actuator is provided, including a cylinder having of a pair of cylinder bodies; a separation wall provided within and between the cylinder bodies, the separation wall defining a pair of pressure chambers within the cylinder; an operation stem located in the axial position of the cylinder; and a pair of pistons provided on the operation stem at different axial positions, each of the pair of pistons being slidably fitted in each respective pair of pressure chambers. The separation wall is made of a cup-shaped member which is provided with a central cylindrical portion in which the operation stem slides, a peripheral cylindrical portion which is secured between the pair of cylinder bodies, and a circular disc portion which connects the central cylindrical portion and the peripheral cylindrical portion.
Preferably, the peripheral cylindrical portion of the cup-shaped separation wall member and the inner wall surface of one of the cylinder bodies are snugly fitted without a seal member therebetween, so that no air leakage occurs between the peripheral cylindrical portion of the cup-shaped separation wall member and the inner wall surface of the cylinder body.
The cup-shaped separation wall member can be formed by press forming sheet metal or by cutting a metal material.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 11-202740 (filed on Jul. 16, 1999) which is expressly incorporated herein by reference in its entirety.